Field of the Invention
The present invention relates generally to devices for obtaining soil samples from below the surface of the ground. In particular, the present invention relates to split tube soil sampling systems.
Description of the Related Art
Methods and practices for collecting representative subsurface soil samples date back many decades. The collection of soil samples is a necessity in some of the following industries: environmental, geotechnical, mineral exploration, and agricultural.
The basic components of a conventional soil sampling assembly 10 are shown in a cutaway view in FIG. 1, and are briefly described below.
A soil sample tube/barrel 11 is typically a cylindrical tube with a threaded connection to a cutting shoe 12 on one end, and a drive head 13 on the other end. The sample tube or barrel 11 provides the space or container that the soil sample occupies once it is collected. It is noteworthy that the cutting shoe 12, sample tube 11, and drive head 13 are usually manufactured with mating threads so that the entire assembly can be threaded and unthreaded in the field.
The cutting shoe or bit 12 is a separate component with a cutting surface 14 at the leading edge of the sampler. The cutting shoe or bit 12 is the component responsible for cutting through the soil as the soil sampler assembly 10 is driven or advanced through the sample interval. It also protects the sample tube (sampler) 11 from being damaged during advancement through the soil sample interval. The cutting shoe or bit 12 is usually considered a consumable part due to the wear of the cutting edge or leading surface. Cutting shoes or bits 12 have several different configurations suited for driving through a variety of soils ranging from soft soils to very hard rock formations. The cutting surface can utilize many different features, such as sharp cutting edges, cutting teeth, carbide buttons, diamond cutters, and many others.
The drive head or sampler head 13 is a component of the overall soil sampler assembly 10 that allows the sampler to be used with various drill rods, probe rods, center rods, or wire line systems. It serves as an adapter so that a common rod or wire line can be used to lower, drive, and retract the sampler assembly. It is common for the head 13 to feature various features, such as check balls, vent holes, and water or air passages.
The soil sampler assembly can also include soil liners (inside the sample tube), solid point assemblies for driving through unneeded soil intervals, and core catchers or core baskets to retain loose soil samples inside the sampler.
The general use and operation procedure for the conventional soil sampling assembly 10 are illustrated in FIG. 2 and are described as follows:
Soil Sampler Assembly and Advancement into Subsurface (i.e. Soil Sample Collection).
The assembled soil sampler 10 can be connected to a common rod, pipe, or casing, and driven or advanced through the sampling interval (usually 1 meter to 60 inches, but can be shorter or longer), as shown in FIG. 2(a). The means for driving or advancing the soil sampler assembly 10 can be percussion, rotation, vibration, static push, or a combination thereof.
Soil Sampler Assembly Extraction from the Subsurface or Borehole
Once the soil sampler assembly 10 has been advanced through the sampling interval, the soil sample has been collected, and the soil sample is occupying the sample tube 11, the soil sampler assembly 10 can be retracted from the borehole B using the connected, drill rod, probe rod, or wire line. FIG. 2(b) shows the empty borehole B after the soil sampler assembly 10 has been retracted; FIG. 2(c) shows the sampler assembly 10 being reinserted into the borehole B after the first soil sample has been removed; and FIG. 2(d) shows the sampler assembly 10 being advanced through a second sampling interval below the first sampling interval.
Soil Sample Removal from the Soil Sampler Assembly
When the soil sampler assembly is retracted from the borehole to ground surface there are a number of methods for obtaining physical access to the actual soil sample inside the soil sampler assembly. The methods and practices for accessing the soil sample inside the soil sampler assembly range from careful and tedious to quickly and carelessly. The latter usually causing the most disruption and damage to the soil sample. It is considered good practice to minimize the disruption to the soil sample. Some of the methods and practices for gaining access to the soil sample inside the soil sampler are as follows:
Soil Liner
One common method to gain access to the soil sample relies on the use of a liner inside the soil sampler assembly (mentioned above). In this case, the liner simply slides out of the end of the sample tube once the cutting shoe or bit is removed. The liner can then be cut with a special cutter in order to gain physical access to the soil sample. While this method is advantageous due to its efficiency and cleanliness, it comes with a monetary cost (i.e., the cost of the liner), and can be limited to softer soils due to the amount of energy needed to collect samples in hard formations. In these cases, the liner can melt or collapse inside the sample tube, thus impeding access to the soil sample.
Vibratory Extraction
In some applications the soil sample is vibrated out of the sample tube using a vibratory oscillator (sonic). This method does not require a soil liner, and therefore eliminates the cost of the liner and allows soil samples to be collected in harder formations such as rock. However, this can cause significant disturbance to the soil sampler due to the violent nature of vibrating the soil out of the sample tube and re-collecting it in another containment item, such as a plastic bag or tray.
Hydraulic/Pneumatic Extraction
This practice is less common since it requires the use of compressed water or air to “urge” or pump the soil sample out of the soil sample tube. In some cases it is advantageous due to its speed, but it is usually avoided due to the high potential for disturbing and damaging the soil sample. An example of this method is outlined in U.S. Pat. No. 6,695,075.
Split Sample Tube/Barrel
This approach relies on the use of a drivable sample tube that can be opened up in order to gain access to the soil sample. It is advantageous since it minimizes disturbance to the soil sample, and it does not require the use of a soil liner (although soil liners can be used with split samplers). Split soil samplers have been on the market for a number of years, an example of which is disclosed in U.S. Pat. No. 7,182,155.
In FIGS. 1, 1A, 1B and 2 of U.S. Pat. No. 7,182,155, an industry standard split sampler is disclosed. It is common in the industry to refer to this design as a “split spoon,” and its construction and method of use are outlined in an ASTM standard. The standard split sampler uses a basic “lap” to align the two sample tube halves, and also utilizes a standard drive head and cutting shoe. While this approach is considered an industry standard, it is limited by its significant decrease in strength when manufactured in longer lengths, such as 60 inches. It is usually manufactured in 24 inch lengths, which makes it very inefficient when many soil samples are needed. It is common to collect soil samples for over 50 continuous feet. This can be done more efficiently if longer (e.g., 60 inch) soil samples are collected.
U.S. Pat. No. 7,182,155 also disclosed a split tube design having a tongue and groove type feature to overcome weaknesses in longer lengths. The tongue and groove construction helps to prevent the sampler assembly from bulging out when driving in hard soils, which is a common problem associated with the “split spoon.” It is not clear if this design is indeed an improvement over the “split spoon” design, but it does have some clear disadvantages. The use of a tongue and groove connection on a tubular component requires a very involved manufacturing process. The nature of this type of connection would likely be problematic when sampling in sandy soils where the sand would penetrate the tongue and groove joint and “sand lock” the two halves of the split sampler together.
There is a need in the industry for an improved split tube soil sampling system.